The invention relates to improvements in the handling of manually operated pneumatic screw drivers.
During the manufacture and assembly of products screw driving operations are frequently necessary, which are performed by the use of manually operated pneumatic screw drivers. Such pneumatic screw drivers are screw driving devices fitted with a compressed air motor and which may be operated using compressed air as a source of energy. The switching on and off of the pneumatic motor takes place manually, as for instance by the actuation of a switch on applying the pneumatic screw driver to a screw to be driven into the work.
It is convenient for the pneumatic screw driver to be suspended on a holding device, which is fitted with a drive means, which is able to produce a lifting force opposing the weight force of the pneumatic screw driver.
It is in this manner that the pneumatic screw driver is suspended in a floating manner and may be drawn downward onto the work to be screwed without any great exertion.
While this type of manually operated pneumatic screw driver does possess many advantages, there are some disadvantages as well. Thus driving in a screw is extremely fatiguing, more particularly owing to the repetitive nature of the operation, and may lead to arm and back pain, something which tends to make for operator negligence, this in turn ultimately leading to a loss in work quality.
One object of the invention is to facilitate and simplify the handling of a pneumatic screw driver when performing screwing operations.
In order to achieve these and/or other objects appearing from the present specification, claims and drawings, in the present invention a device for the control of the thrust force of a manually operable screw driver suspended by means of a holding means in a vertically moving manner comprises a drive means for applying a lifting force opposing the weight force of the pneumatic screw driver and control means adapted to cause a reduction or switching off of the lifting force due to the drive means responsive to a certain drop in the operating pressure for the pneumatic screw driver.
Accordingly for screw driving operations may be performed extremely ergonomically with no operator fatigue, something which leads to high quality products despite long periods on the job. The invention is based on the discovery that during the operation of a pneumatic screw driver the operating pressure supplied to it is subject to a slight drop, which is detected by the control means and may be employed as a trigger to reduce the lifting force caused by the drive means or even to switch it off completely.
The result of this is that directly after putting it into operation of the pneumatic screw driver the weight force thereof and possibly the weight forces loading the pneumatic screw driver of the holding device are no longer compensated so that the thrust force, with which the pneumatic screw driver is thrust downward against the screw to be driven, is increased substantially without the application of force by the operator. In the case of a complete switching off of the lifting force the pneumatic screw driver will be urged with its entire weight force against the screw to be driven so that the operator is substantially relieved. If it is a question of a pneumatic screw driver which is activated by being thrust against the screw with a certain force, the system may be so set that the operator only has to apply the thrust force necessary for activation during the entire screwing operation, whereas the greater thrust force necessary for the screw driving operation is then provided by the system.
Further advantageous developments of the invention are defined in the claims.
After the termination of a screwing operation and deactivating of the pneumatic screw driver the operating pressure will immediately rise to the initial value. The control means are preferably able to cause a renewed increase or a renewed switching to a higher value of the lifting force is responsive to such a pressure increase so that after switching off of the pneumatic screw driver the same conditions will obtain as before putting it into operation. The vertical motion of the pneumatic screw driver is therefore aided to the required degree after stabilization of the operating pressure.
For the detection of the drop in pressure the control means will preferably comprise a pressure sensor which is placed in the air supply line supplying compressed air to the pneumatic screw driver for the operation thereof. In this respect the pressure sensor may be provided both in the line component extending outside and also inside the pneumatic screw driver. More particularly, there is also possibility of integrating the pressure sensor directly on the pneumatic screw driver or in the same.
As a drive means a single acting or a double acting power cylinder is more particularly provided, in the case of which it is preferably a question of a pneumatic cylinder. It comprises a working chamber able to receive a drive fluid and more particularly compressed air, for causing the lifting force, the control means comprising a control valve means, which in a fashion dependent on the pressure level of the operating pressure influence the pressure obtaining in the working chamber.
It is preferred for the control means to be coupled with a pressure sensor to cooperate therewith to produce a control function, said pressure sensor being placed in the air line supplying the pneumatic screw driver with the operating pressure so that it is operated in a manner dependent on the signal produced by the pressure sensor.
The control valve means may comprise a pressure regulator. Same may be more particularly employed to adjustably set the degree of reduction of the lifting force.
Preferably, the pneumatic screw driver is arranged on a parallelogram linkage in the holding device and is seated more particularly on a receiving means which may be lowered and lifted without changing its spatial orientation so that the pneumatic screw driver as well will always have the same alignment.